Hollar S. (editor) A Closer Look at Biology, Microbiology, and the Cell

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A closer look At BIology, MIcroBIology, And the cell

Areas of Study

Microbiologists classify microorganisms

into bacteria, protozoans, algae, fungi, and

viruses, and the study of each constitutes

a separate specialty within microbiology.

Individual ﬁelds may overlap, and the disci-

pline of microbiology may overlap with other

disciplines, as it does with immunology. In

any case, most areas of scientiﬁc inquiry can

be subdivided in a variety of ways, depending

on the questions being asked. Microbiology

may be subdivided as follows.

Bacteriology

The study of bacteria is called bacteriology.

Bacteria are single-cell microbes that grow

in nearly every environment on Earth. They

are used to study disease and produce anti-

biotics, to ferment foods, to make chemical

solvents, and in many other applications.

Protozoology

Protozoology is the study of protozoans,

small single-cell microbes. They are fre-

quently observed as actively moving

organisms when impure water is viewed

under a microscope. Protozoans cause a

number of widespread human illnesses, such

as malaria, and thus can present a threat to

public health.

Phycology and Mycology

Phycologists study algae. In general, algae are

organisms that are made up of one or more

eukaryotic cells (cells with a true nucleus)

that contain chlorophyll and that are less

complex than plants. Mycology is the study

of fungi—well-known organisms that lack

chlorophyll, as well as the organized plant

structures of stems, roots, and leaves. Fungi

usually derive food and energy from parasitic

growth on dead organisms.

Virology

Viruses are a vastly different kind of bio-

logical entity. They are the smallest form

of replicating microbe. Viruses are never

free-living; they must enter living cells to

grow. Thus they are considered by most

microbiologists to be nonliving. There is

an infectious virus for almost every known

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Exobiologists search for traces of microbial life in rock samples from

Mars and other planets. NASA/JPL-Caltech/University of Arizona

kind of cell. Viruses are visible only with the

most powerful microscopes, namely electron

microscopes.

Exobiology

Exobiology is the study of life outside the

Earth, including that on other planets. Space

probes have been sent to Mars, and samples

A closer look At BIology, MIcroBIology, And the cell

of rocks have been brought back from our

moon as part of experiments to search for

traces of microbial life in extraterrestrial

environments. Most exobiologists examine

such samples for the basic building blocks

of life known to have evolved on Earth.

Because microbes were probably the earliest

organisms on Earth, and because they have

continued to thrive, exobiologists consider

microbes to be the most likely form of life to

exist beyond the Earth.

Biological Warfare

Another area of study in microbiology

involves the development, deployment, and

defense against agents of biological warfare.

Both chemical and biological agents have

been used in past wars because they are often

more insidious and less easily detected than

conventional weapons. This application of

microbiology has been made still more omi-

nous by the ability to alter microbes using

genetic engineering.

Methods of Microbiology

The chief tool of the microbiologist has

always been the microscope. Since its

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invention there have been great reﬁnements

in the optical microscope’s power and preci-

sion. In addition, the electron microscope

and other high-energy devices allow micro-

biologists to view the smallest structures of

life, including the DNA molecule. However,

because the powerful forms of energy that

are necessary for electron microscopes, such

as X-rays and particle beams, will destroy

biological specimens, scientists have devel-

oped new technologies for viewing cells.

The transmission electron microscope, for

example, produces a shadow of the speci-

men by evaporating platinum metal over the

viewing platform at a sharp angle. When elec-

trons are passed through the platform at high

speed, they can distinguish the shadows on

the metal as a representation of the original

specimen. Scanning electron microscopes,

however, view the surface of a specimen by

reﬂected radiation. In this case, the sample is

also thinly coated with a heavy metal such as

gold, and the biological material is observed

as a cast of the more stable material. The

various types of electron microscopes have

allowed microbiologists to study in detail the

ﬁne structures of bacteria and viruses. With

continued reﬁnements and the development

of new technologies in microscopy, it may

A closer look At BIology, MIcroBIology, And the cell

Electron microscopes give microbiologists the ability to view minus-

cule structures like chromosomes. Shutterstock.com

eventually prove possible to view individual

genes or protein molecules within a cell.

Advances have also occurred in the use of

pure cultures, and improvements in methods

of growing and identifying microbes have

found wide application in all areas of microbi-

ology. In the laboratory, scientists must have

pure cultures of microbes for their studies.

If contaminating organisms are present, the

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The Work of

Microbiologists

Professional microbiologists are employed

in a wide variety of positions. The majority

work in universities, government agencies, or

industry. In colleges and universities, micro-

biologists teach and conduct research. State

and federal governments employ micro-

biologists to conduct research and to help

regulate private-sector activities. For example,

in the United States some microbiologists are

employed by the federal government to inspect

sewage-treatment facilities, hospitals, and

food-production plants to protect the pub-

lic health. Large federal agencies, such as the

National Institutes of Health, the Department

of Agriculture, and the Centers for Disease

Control also employ microbiologists to inves-

tigate and monitor the action of microbes in

our environment. There are also many com-

mercial positions available to microbiologists.

For example, wineries and breweries employ

microbiologists to help standardize and main-

tain yeast cultures. In many other areas of

industrial food production, the expertise of

microbiologists is employed in quality control

to guard against spoilage and contamination.

Microbiologists are also employed by pharma-

ceutical companies to help produce vaccines

and other drugs.

A closer look At BIology, MIcroBIology, And the cell

results of their experiments may be useless

or misleading. For these reasons, microbi-

ologists maintain pure cultures of the known

microbes and provide them to associates for

experimental use.

History of Microbiology

Microbiology began with the development

of the microscope in the 17th and 18th cen-

turies. By 1680 Anthony van Leeuwenhoek

had produced a simple hand-held device

that allowed scientists to view a variety of

microbes in stagnant water and in scrapings

from teeth. In the late 1700s Edward Jenner

conducted the ﬁrst vaccinations, using cow-

pox virus to protect people against smallpox.

Later an altered form of the rabies virus was

used to protect against the dreaded disease

rabies. Vaccines remain the major means of

protection against most viral infections.

Modern microbiology had its ori-

gins in the work of the French scientist

Louis Pasteur—considered the father of

microbiology—who developed methods

of culturing and identifying microbes.

During the second half of the 19th cen-

tury, he and his contemporary Robert Koch

provided ﬁnal proof of the germ theory

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of disease. They also demonstrated that

microbes must be introduced or seeded

into a sterile environment and could not

arise spontaneously, as had been previously

believed. Pasteur was the ﬁrst to propose

that microbes cause chemical changes as

they grow. Koch derived a central principle

of modern microbiology, known as Koch’s

Postulate, that determines whether a par-

ticular germ causes a given disease.

Pasteur and his contemporaries devel-

oped pure culture methods for the growth of

microbes. By diluting mixtures of microbes

in sterile solutions, they were able to obtain

droplets that contained a single microbe,

which could then be grown on fresh, sterile

media. In a separate procedure, they used

rapid, sequential passage of cultures so that

certain specimens were able to outgrow oth-

ers. Thus, for the ﬁrst time, stable cultures

containing a single kind of microbe could be

used to identify and study speciﬁc disease-

causing organisms.

Another great advance in pure culture

methods came in the late 19th century,

when microbiologists discovered that each

kind of microbe preferred a certain medium

for optimal growth. Over the past century,

microbiologists have made great progress in

A closer look At BIology, MIcroBIology, And the cell

Alexander Fleming discovered that the mold Penicillium prevents the

growth of bacteria. Hemera/Thinkstock

the preparation of selective media for the

puriﬁcation and identiﬁcation of most spe-

cies of microbes.

In 1929 Alexander Fleming observed that

molds can produce a substance that pre-

vents the growth of bacteria. His discovery,

an antibiotic called penicillin, was later iso-

lated and produced commercially to protect

people against the harmful effects of certain

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